A theoretical analysis method for stiffened deep cement mixing (SDCM) pile groups under vertical load in layer soils

A theoretical analysis method is proposed to forecast the vertical bearing behavior of a long-core SDCM pile group. The load-settlement behavior of a long-core SDCM pile group is different from that of a single long-core SDCM pile due to the existence of the pile group effect. In this study, the nonlinear behaviors of the inner core–cemented soil interface and the inner core–soil interface are expressed via exponential models, whereas the nonlinear relationships of the cemented soil–soil interface and the pile base–soil interface are calculated via an elastic–plastic model. Additionally, the soil between piles is considered a medium that generates additional displacement. Based on the above conditions, the interaction between long-core SDCM pile groups was analyzed. This method was first used on a single long-core SDCM pile, and the results were compared with the analytical solutions and FEM results from previous studies; then, the field test results of long-core SDCM pile groups were compared. A reasonable prediction can be achieved via the method proposed in this article. Finally, the law of additional displacement caused by the pile group effect and the optimal solution for the cemented soil coverage size for the long-core SDCM pile group were obtained by analyzing important parameters, including the pile spacing s_ij, the height ratio of the cemented soil to the PHC pipe pile L_c/L_p, the radius ratio of the cemented soil to the PHC pipe pile R_c/R_p, and the slenderness ratio L/R_c.